Final Fantasy XV has these issues

The first Final Fantasy of the mainline that I played was Final Fantasy VII but the first Final Fantasy that I completed was Final Fantasy XIII. At that time I didn't really know anything about the Final Fantasy series and it's extreme success in Japan as well as overseas. Hence I also had no knowledge of the high standards of the fanbase since they always expected the best experience when it comes to a Final Fantasy game. Final Fantasy XIII was a good game but it just didn't satisfy the fanbase (at least the majority weren't.). If you look closely the script was a little bit off and at times cheesy and the gameplay was a turn-based system that tried to look like an action-based one. The villain wasn't a memorable one and didn't really had any legitimate motives for his cause and at times even did completely irrational and stupid stuff (R.I.P. Jihl). The developers also did a half-assed job with the visuals what was actually pretty unusual for a game made by SE (you can hate games made by SE however you want but if there is one thing that one cannot criticize then it would be the visuals of the game).

The game didn't push the tech on which it was built on to it's limits and the developers didn't really try to improve the game as a whole (,,Final Fantasy disease'' is what he called it). BUT afterwards I do believe that the developers tried to improve themselves with the sequel of Final Fantasy XIII. The script was better , you had a more memorable villain (Caius seriously needs a hug) and a conflicted protagonist and both of them wanted the same but their modus operandi was different. I enjoyed the gameplay more than it's predecessor and all in all the experience was better. Yet the fanbase still proceeded with shredding that game to pieces as well. It still didn't live up to their expectations.

The problem lies in the jump into the HD era. Up until that point all of the Final Fantasy games were turn-based games but nowadays turn-based games just do not appeal to a gamer due to the visuals. When the fanbase was newly introduced to Final Fantasy XIII they considered a turn-based battle system to be a core element of Final Fantasy which is why the devs were hesitant to suddenly introduce them to an action-based battle system. Thus the half assed battle system was born. I actually d not have any issues with Lightning Returns when compared to Final Fantasy XIII. imo the script was better and the gameplay more enjoyable and it seemed like the devs finally took the plunge into the direction of action-based games. But at that point the fanbase , who were clouded by their nostalgia, criticized the trilogy for the sake of criticizing. The Final Fantasy XIII trilogy already had a blank future because of the fanbase and even Final Fantasy XV has these issues (although the amount of people who can't let go of their nostalgia are the extreme minority). There are even people who want the Final Fantasy VII remake to be turn-based.

Conclusion: Final Fantasy XIII received hate due to the Final Fantasy disease or rather the Final Fantasy virus. People refused to let go of their nostalgia and didn't accept the new approach of the developers. Thus the developers were intimidated of changing the franchise because of which the quality of the game suffered.